Sustainable management of textile waste and dye pollution: Waste cotton-derived nitrogen-doped biochar for enhanced environmental remediation and resource recovery.

This study presents a sustainable strategy to convert waste cotton textiles into nitrogen-doped biochar via one-pot pyrolysis with KOH activation and urea doping. The optimized NBC exhibited a high specific surface area of 1037.8 m2/g and well developped pores structure, achieving a remarkable methylene blue adsorption capacity of 540.54 mg/g. Kinetic and isotherm analyses, together with FT-IR and XPS results, revealed that adsorption was governed by pore filling, π-π interactions, and enhanced surface affinity due to nitrogen-containing functional groups. The NBC also demonstrated good reusability, retaining approximately 90% of its initial adsorption capacity after five consecutive adsorption-desorption cycles. Beyond the adsorption performance, the NBC showed promising electrochemical properties, with specific capacitance increasing from 150 F/g to 375 F/g at 3 A/g, revealing its potential as an electrode material. Notably, the electrode exhibited good long-term cycling stability, maintaining 78.6% of its initial capacitance after 5000 cycles. Density functional theory (DFT) calculations further elucidated the distinct roles of different nitrogen configurations: pyridinic N creates electron-rich sites for adsorption, while graphitic N improves overall charge conductivity. This work offers a practical route for co-managing textile waste and dye wastewater, transforming a low-value waste into a multifunctional carbon material for environmental and energy-related applications.